Of all the elements that comprise a mobile audio system, it is the crossover that is perhaps the most misunderstood – and there’s a justifiable reason for that.

On the other end of the spectrum, it’s the subwoofer that gets the most attention, as this is the “sexier” aspect of a mobile audio system, what with a sub’s ability to shake a car’s foundation to the point everyone in the street can hear it coming. In-between are pieces like the head unit, maybe a CD player, amplifiers and equalizers, but when it comes to the crossover, knowledge gets hazy and interest goes by the proverbial wayside.

Why are crossovers so misunderstood or otherwise ignored?

The right-to-the-point answer is this: Since, depending on the system being planned, they may not be absolutely necessary, it’s easy to just overlook them altogether. Still, that doesn’t mean that crossovers aren’t important; in fact, in order to answer the question we posed in the beginning of this post regarding whether or not someone needs a crossover in car audio, a couple of rudimentary principles at the beating heart of mobile audio crossover usage is in order.

It’s a range of audio frequencies, running the full spectrum of human hearing, that comprise what we know as music, yet some speakers have been designed to better reproduce certain frequencies than others.

Tweeters, for example, are designed to deliver clean “high” frequencies (or the traditional “treble” sounds) while woofers are specifically engineered to reproduce bone-rattling “low” frequencies.

As we covered in previous posts, basic systems that use so-called coaxial speakers boast small crossovers already built into the drivers, while other systems – notably ones that use component-style speakers – typically take advantage of external crossovers that transfer only the right frequencies to the appropriate drivers.

What’s the point here? The primary purpose of dividing musical signals into independent frequencies by routing particular frequencies to certain speakers is to achieve improved fidelity. Ensuring that only the correct frequencies are delivered to the right speakers virtually guarantees that distortion is reduced, and that the system’s overall sound quality is enhanced.

So, with that background in mind, who really needs a crossover?

As we hinted at earlier, it may be possible to install a system with no additional crossovers in a basic system configuration. In the same way that many receivers (head units) include a built-in (albeit low-powered) amp, it is possible for speakers to come with built-in crossovers; however, there are a number of instances where either an active or passive unit will improve sound quality, system efficiency – or both.

If you’re running a mobile audio system that uses coaxial speakers, an additional crossover won’t be necessary because such full-range speakers already boast built-in passive crossovers which handle filtering of the frequencies that go to each driver.

On the other hand, you will probably need one or more crossovers if the plan is to build a component speaker system complete with multiple amplifiers and subwoofers, as you will have to keep “unwelcomed” frequencies from arriving at certain speakers.

How to Choose a Crossover

It essentially comes down to either an active or passive approach. Passive crossovers don’t need power to filter the signal as desired, while active crossovers demand power and ground connections; with active crossovers, you’re given more flexibility and fine-tuning control over your music.

Some other things to keep in mind

Active Systems

A sound system is dubbed “active” if each driver (tweeter, woofer, sub) has its own channel of amplification, dramatically increasing available power, dynamic range and control of the system’s tonal response over the whole audio spectrum. An active crossover, with regard to an active system, gets wired between the receiver (head unit) and amp, and cuts out the unwanted frequencies before the amp wastes energy boosting them.

Passive Component Crossovers

These step into the signal path after the amplifier as small networks of capacitors and coils, normally installed near the speakers. While component speaker systems come with their own crossovers set for optimum performance, as we have covered, there are so-called passive component crossovers that boast optional settings that allow you to turn down the tweeter if it seems to be overpowering the woofer.

In-Line Crossovers

There are also in-line crossovers that connect before the amplifier; these cylinder-looking devices have RCA connectors on each end and simply plug into an amp’s inputs to ensure the amps don’t waste energy, say, amplifying high frequencies to a subwoofer amp.

If you plan on expanding your system in the future, it’s best to choose a separate outboard crossover rather than relying on the variants built into an amplifier and head unit.

How to Set a Crossover

Varying your crossover points is essential to “tuning” your system and speakers, and crossovers bring this kind of adjustability. At a basic level, setting your low-pass filter above 100Hz provides you the type of bass boom many hip hop music fanatics seek, while pushing it down to 80Hz tightens up the bass and improves front soundstaging.

The following videos provide step-by-step details about setting a crossover:

Conclusion

The answer to the question, “What is a crossover, and what exactly do they do?” lies within the word itself: “Crossover” comes from the concept of “crossing over” from one frequency range to the next, and in car audio, the crossover serves as a filter that blocks out unwanted frequencies to a speaker or group of speakers. Our hope is that this article serves as a blueprint for deciding on the proper type of crossover for your system, all dependent on what you’re trying to achieve and the equipment you’re choosing.

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